Consider the following information:
Bob pushes against a rock of mass 50 kg for 20 minutes exerting an average force of 100 N but the rock never budges. He really wants to move the rock so he asks his wife Barbara to come out and help. She pushes on the rock with another 100 N and eventually the rock starts to move. As the couple keeps pushing, it becomes easier and easier to move.
At the end of the driveway is a ledge and the couple push the rock off the ledge. The rock falls for 3 seconds and eventually crashes into the riverbed below.
According to a physicist, work is defined as the force applied to an object multiplied by the distance the object moves during the time the force is applied. Using this definition, how much work did Bob do before Barbara helped him?
Explanation
Work is defined as the force (F) multiplied by the distance moved (d). Since the rock didn’t move, the work done is zero. Choice (A) is correct.
Employees at GetWell research labs are analyzing mechanical waves, which require a medium to pass through, and electromagnetic waves, which travel through space. Jose Gonzalez IV is studying electromagnetic waves and their potential, real-world health and medical applications. He records the lengths of the various waves, noting that radio waves are the longest, while Gamma rays are the shortest. When calculating the frequency of the wave, or the number of wavelengths that occur in a distinct amount of time, Jose notes that there is an inverse relationship between the frequency of a wave and its period, which is the time it takes for a single wave to occur.
Wave type | Wave length size | Application |
Radio Waves | Grater than 30cm | Aircraft Naviagtion, TV, AM/FM Radio |
Infrared Waves | 30cm - 1mm | Microwave Ovens, Mobile Phones |
Visible Light | 1mm - 700nm | Remote Controls, Toasters, Night Vision |
X-Rays | 700nm - 400nm | Physical Therapy, Light Bulbs, Photography |
Ultraviolet Light | 400nm - 60 nm | Sanitation, Air Purification, Forgery Detection |
X-Rays |
60nm - \(1 \times 10^{4}\)nm |
Medical Examination, Cancer Treatment |
Gamma Rays | 0.1 nm - \(1 \times 10^{5}\) nm | Cancer Treatment, Food Irradiation |
Based on the information provided, which types of waves have potential medical applications? Choose all that apply.